1. Field of the Invention
The present invention relates to a gas purifying system, and more particularly, to a gas purifying system for effectively eliminating contaminating materials emanating from production equipment, equipment operators, and the ambient production environment in general.
2. Description of the Related Art
Particulate contamination during the semiconductor device manufacturing process greatly increases the likelihood of device failure. In particular, a highly purified gaseous atmosphere is required to control fine particles (i.e., atomic or molecular sized gaseous contaminating particles) on or near the surface of a semiconductor substrate. The sources of these contaminating particles are numerous, including the production equipment, the equipment operators, the ambient production environment, and the process gases, acids and bases, organic contaminants, etc., used in manufacturing a semiconductor device.
Purification systems are thus very important for the productivity and proper operation of a semiconductor device, and many methods are employed to control or eliminate contaminating particles.
For example, semiconductor devices are manufactured and managed in a clean room. In the clean room, various filters, water showering systems (WSS), etc. are employed to collect and remove the contaminating materials. Generally, about 400-600 filters are installed in a single clean room.
Filters employed in the clean room are typically active carbon filters or ion exchange filters (IEF). The active carbon filter is manufactured by pulverizing active carbon, compression molding the pulverized active carbon, and then coating a material thereon which attracts or collects a specific contaminating component. The active carbon filter is utilized for removing ozone, organic materials, SOx, NOx, etc. The IEF filter is manufactured by combining fiber with various chemical functional groups and is utilized for collecting ions such as ammonium cation.
The WSS produces minute water droplets formed by spraying water through nozzles. Floating dust within an air stream collides with these water droplets and become adsorbed, and then they are eventually removed.
FIGS. 1A and 1B are schematic diagrams of a conventional WSS in which FIG. 1A is a side view and FIG. 1B is a partial top view taken along a line 1-1xe2x80x2 in FIG. 1A. The conventional WSS includes the following: a water spraying system 10 having a plurality of nozzles 14a, 14b, 14c, etc., for producing minute water droplets; a crash plate 20 for separating the water droplets into minute droplets having a smaller size than the water droplets; an eliminator 30 with which the water droplets collide and then fall downward; and a tank 50 for collecting the falling water droplets and storing this collected water until the collected water is provided to the water spraying system 10. In operation, potentially contaminated in-flowing air Ai is introduced into the WSS through the water spraying system 10, it passes through the crash plate 20 and the eliminator 30 along a path designated by the arrows, and it is then exhausted out as clean out-flowing air Ao.
The water spraying system 10 is provided with a plurality of vertically extending water transferring pipes 12a, 12b, 12c, . . . 12n, and a plurality of nozzles 14a, 14b, 14c, . . . 14n, configured in at least one vertical line on each of the water transferring pipes. A water transferring pipe supporter 16 supports the water transferring pipes 12a, 12b, 12c, . . . 12n. 
Water supplied from the tank 50 by means of a pump 60 moves upward along the water transferring pipes 12a, 12b, 12c, . . . 12n, and then is rapidly sprayed through the nozzles 14a, 14b, 14c, . . . 14n. In this embodiment the nozzles are arranged in two vertical columns on the water transferring pipes, preferably with a predetermined angle larger than 90xc2x0 separating the columns. The size of the sprayed water droplets can be controlled, and is determined by the size of the nozzles 14a, 14b, 14c . . . 14n, and the water pressure. Preferred droplet size is about 100 xcexcm or less for optimal effect in removing the contaminating material.
The water droplets sprayed from the nozzles 14a, 14b, 14c . . . 14n, impact the crash plate 20, which comprises a plurality of vertically extending long plates 22a, 22axe2x80x2, 22b, 22bxe2x80x2, . . . 22n, 22nxe2x80x2 so that the water droplets are divided into smaller droplets. When the size of the water droplets becomes smaller, the overall effective surface area of the group of droplets becomes larger. Thus, the adsorbing effect of the droplets for the contaminating material increases. For each of the water transferring pipes (e.g., 12a), two corresponding plates (e.g., 22a, 22axe2x80x2) are installed. The plates 22a, 22axe2x80x2, 22b, 22bxe2x80x2, . . . 22n, 22nxe2x80x2 are supported by a crash plate supporter 26 and are provided perpendicular to the direction of the sprayed water from the nozzles (e.g., 14a) as shown in FIG. 1B.
Water droplets, which have passed through the crash plate 20, collide with the eliminator 30. The eliminator 30 is manufactured from a plastic material or SUS (stainless steel) and preferably has a porous plate shape. The eliminator 30 comprises a plurality of eliminating plates 32a, 32b, 32c, . . . 32n, as shown in FIG. 1B. The eliminating plates 32a, 32b, 32c, . . . 32n, are installed so that the openings through the adjacent eliminating plates are offset, and are supported by an eliminator supporter 36. In such an arrangement, water droplets containing contaminating material passing through a front eliminating plate 32a might collide with a rear eliminating plate 32b or 32c. 
Since it is positioned under the water spraying system 10, the crash plate, 20 and the eliminator 30, the tank 50 collects the water droplets containing the contaminating materials, which have collided with the crash plate 20 and the eliminator 30. The collected water is stored in the tank 50 until the water is provided to the water spraying system 10 again. The recirculation time is determined by periodically measuring the electrical resistance of the water in the tank 50. When the water contains a large amount of contaminating material, the resistance thereof increases. Generally, a predetermined amount of water is injected while the same amount of water is exhausted out to keep the resistance of the water at a constant value.
By utilizing the above described filtering and WSS gas purifying systems, various contaminating components including floating dust and aqueous contaminating materials can be advantageously removed.
However, non-aqueous contaminating materials and organic contaminating materials cannot be satisfactorily removed. In particular, when a large amount of gas passes rapidly, the contaminating material contained in the gas also passes rapidly, which minimizes the amount of time the contaminating material can impact the water droplets. In addition, for sub-micron particles, the removing efficiency of the non-aqueous and organic gas contaminating materials and minute particles is poor.
Indeed, among the causes for deterioration in production yields of semiconductor devices, it is believed that 80% or more are caused by minute particle contamination. As the integration density of semiconductor devices increases, tighter controls on gaseous contaminating materials is required. Furthermore, since the lifetime of the above-described filters and WSS is limited, replacement of the filters, and the maintenance/upkeep of the nozzles and eliminator are required.
Research is being conducted on gas purifying systems utilizing ultraviolet light. According to this principle, photoelectrons generated by an ultraviolet ray attach themselves to the minute particles in the air, and this combination is then collected by an electrode. Japanese Laid-Open Patent No. Hei 6-252242 discloses a gas purifying system including a photoelectron emitting material, ultraviolet source and/or an exposing light source, and an electrode in a closed space. In this system, the particles in the air are charged by the photoelectrons generated by the ultraviolet light and then collected by the electrode.
Japanese Laid-Open Patent No. Hei 4-239131 discloses a method of charging minute particles on the surface and near the wafer by exposing the minute particles to an ultraviolet ray and collecting the charged particles to remove them. U.S. Pat. No. 5,380,503 discloses a method of purifying gas in an isolated space. In this patent, an electric field is formed between an electrode and a photoelectron emitting material. Particles in the space attach to the photoelectron generated from the photoelectron emitting material by an ultraviolet lamp, and are then collected by an electrode.
However, since the above-described methods are applied in the isolated space, the instruments are small. Accordingly, these systems are mostly used for cleaning a small limited space in which high purity is very important, such as a space used for storing goods.
In view of the above, it is an object of the present invention to provide a gas purifying system by which molecular contaminating materials, including non-aqueous and organic contaminating materials as well as aqueous contaminating materials, can be advantageously removed.
To achieve this and other objects, the present invention provides a gas purifying system including a water spraying system. A collecting apparatus is installed at the rear portion (downstream) of the water spraying system. The surface of the collecting apparatus is manufactured from a material that can emit electrons when subjected to visible light, ultraviolet light, or electrical energy.
According to the present invention, aqueous contaminating materials and floating dust can be initially removed by the minute water droplets in the water spraying system, and then organic and non-aqueous contaminating materials can be secondarily removed by an interaction of the water droplets with the electrons.